I keep hearing people say this about Sanders but no one seems to be saying the equivalent about Trump.
You're not listening very well.
“Republicans are looking at him and starting to think, ‘Maybe I could swallow him,’ and independents are looking at him going, ‘Oh my god, I can’t believe it,’”
http://www.theatlantic.com/politics/archive/2016/01/why-the-trump-gap-is-growing/458760/